Low-temperature Liquid Exfoliation of Milligram-
scale Single Crystalline Few-layer β12-Borophene
Sheets as Ecient Electrocatalysts for Lithium–
Sun Yat-sen University
Dalian Institute of Chemical Physics, Chinese Academy of Sciences
Dalian Institute of Chemical Physics
Shanxi University https://orcid.org/0000-0002-0162-5091
Shanxi University https://orcid.org/0000-0001-5666-0591
Dalian University of Technology
Dalian Institute of Chemical Physics
Bing Yang ( firstname.lastname@example.org )
Dalian Institute of Chemical Physics https://orcid.org/0000-0003-3515-0642
Dalian Institute of Chemical Physics, Chinese Academy of Sciences https://orcid.org/0000-0003-1851-
Sun Yat-sen University https://orcid.org/0000-0001-7603-9436
Keywords: Two-dimensional (2D) borophene, lithium sulfur (Li-S) batteries, low-temperature liquid
exfoliation (LTLE) method
Two-dimensional (2D) borophene is predicted as an ideal electrode material for lithium sulfur (Li-S)
batteries because of low-density, metallic conductivity, high Li-ion surface mobility and strong interface
bonding energy to polysulde. But until now, 2D borophene-based Li-S batteries have not yet been
achieved due to the absence of massive synthesis method. Herein, we developed a novel low-temperature
liquid exfoliation (LTLE) method for scalable synthesis of single crystalline 2D few-layer
sheets with a symmetry. The as-synthesized 2D sheets were used as the polysulde
immobilizers and electrocatalysts of Li-S batteries for the rst time. The resulting Li-S cells employing
borophene sheets delivered a strikingly high areal capacity of 5.2 mAh cm− 2 at a high sulfur loading of
7.8 mg cm− 2 with an ultralow capacity fading rate (0.039 % per cycle) in 1000 cycles, outperforming
most of the Li-S batteries employing other 2D materials. Under the help of few-layer
high-activity behaviors should be attributed to the signicant enhancement of both the Li-ion’s surface
migration and the adsorption energy for Li2Sn clusters based on density functional theory (DFT) models.
Our research reveals great potential of 2D
12-borophene sheets in future high-performance Li-S batteries.
The rapid development of electrochemical energy storage devices in the elds of electric vehicles,
portable electronic devices and large-scale smart power grids continuously drive the researchers to
explore lower cost, higher energy density, and better safety batteries than current lithium-ion batteries1-4.
Among many candidates, lithium sulfur (Li-S) batteries have been gaining the global attention due to their
overwhelming energy density (2600 Wh kg-1), natural abundance and environment-friendly of sulfur
feedstock5-9. However, the existence of internal polysulde shuttling, large volume expansion of sulfur
and sluggish redox kinetics inevitably lead to the sharp deterioration of the electrochemical performances
of Li-S batteries10-12.
Considering the irreversible loss and inecient utilization of sulfur cathodes, much effort has been
devoted to the design of advanced materials for immobilizing and activating sulfur materials, such as
transitional-metal oxides13,14, suldes15-17, carbides,18-20 metal nitrides21-23and heterostructures24-26.
Recently, two-dimensional (2D) materials with strong in-plane covalent bonds and weak interlayered van
der Waals (vdW) forces have been intensively studied because of their superior advantages over
traditional bulk materials for Li-S cell applications27,28. 2D materials such as siloxane29, black
phosphorene30,31, BN32,33, C3N434,35, and MXene36,37, were found to exhibit excellent catalytic activities
towards polysuldes because of their extraordinary surface properties. However, most of these 2D
material-based Li-S cells still have some disadvantages, such as low capacity38, slow charge-discharge
rate39,40, structure instability38,41, and poor cyclic stability32. Hence, the design and development of novel
2D materials are highly demanded towards high-performance Li-S batteries with large catalytic activity,
high-ecient adsorption, fast conversion of polysuldes and long-term durability.
As a typical 2D Dirac material consisted of the lightest solid element, 2D borophene with unique surface
conguration and complex multicenter-two electron bonds has been earlier predicted as an ideal
electrode material for Li-S batteries due to its native metallic conductivity42, large elastic modulus43,
heavy anisotropy44, high Fermi velocity(6.6×105 m/s) 45, excellent thermal and chemical stability46, large
Li-ion surface mobility as well as strong bonding energy to polysulde clusters47. However, borophene-
based Li-S cells have not yet been achieved for practical use so far owing to the absence of a facile route
for the scalable production of 2D borophene nanomaterials.
In this work, we developed a low-temperature liquid exfoliation (LTLE) strategy for scalable production of
single crystalline borophene sheets as ecient polysulde electrocatalyst for Li-S batteries. Few-layer 2D
borophene sheets with
12-phase were thus identied with an average ake size of ~3 μm and an
ultrathin thickness less than 10 atomic layers. The
12-borophene sheets exhibited extraordinary
performances as ecient immobilizer and electrocatalyst for advanced Li-S batteries, showing excellent
rate performance of 721 mAh g-1at 8 C (1 C = 1675 mAh g-1) and an ultralow decay rate of less than
0.039 % in 1000 continuous cycling measurements. More impressively, the areal capacity can arrive as
high as 5.2 mAh cm-2 at a large sulfur loading of 7.8 mg cm-1 in lean electrolyte with a ratio of electrolyte
to sulfur (E/S) ratio of 6.8 ml g-1. Our work suggests that single crystalline few-layer borophene sheets
hold great potential for high-eciency Li-S batteries.
Results And Discussions
The LTLE synthesis process of few-layer borophene sheets is schematically illustrated in Fig.1a. By
optimizing the sonication power and solvent concentration, massive production of 2D borophene sheets
has been successfully achieved. N-methyl pyrrolidone (NMP) was found to be the most effective among
a series of solvents adopted in our experiment, as seen in Supplementary Figs.1 and 2. The color of the
product solution is dark-brown or dark-black in Fig.1b, varying with the sheet concentration. Moreover, the
mass of 2D sheets reaches as high as 10 mg and their yield is over 20 %, evidently increased compared
with previous reports (≤ 10 %48,49). The low-temperature approach is thus believed to improve the
exfoliation eciency of non-layered bulk materials, because of which signicantly enhances the
anisotropy discrepancy between the in-plane and out-of-plane covalence bonds50. Scanning electron
microscope (SEM) and atomic force microscope (AFM) images of the as-grown products are respectively
in Fig.1c, d, where ultrathin 2D borophene sheets are observed to have an edge length of 2 ~ 5 µm and
exhibit uniform and smooth appearance. The thickness of 2D sheet is observed to be only 1.32 ~ 2.32
nm, suggesting its ultra-thin nature.
X-ray diffraction (XRD) pattern of 2D borophene sheets (Supplementary Fig.3) shows the same
characteristic diffraction pattern as that of the theoretically calculated
12-borophene using density
functional theory (DFT), clearly different from that of the bulk
-rhombohedral boron powder (JCPDS No.
00-031-0207). As seen in Fig.1e, the X-ray photoelectron spectrum (XPS) of B 1s core level is consisted of
two characteristic components, attributed to the B-B species at 187.5 eV51 and the B-O species at 189.1
eV52, respectively. And the molar ratio of the B-B to B-O species is estimated to be more than 94 %,
suggesting a majority of pure boron composition in 2D borophene sheets. The minor B-O species are
supposed to originate from the edge oxidation of borophene sheets during the short exposure to the air
after being taken out for XPS measurements (Supplementary Fig.4)52.
Raman spectroscopy was employed to better differentiate the 2D borophene sheets from the bulk boron
powders53,54. Four Raman peaks of 2D borophene sheets are clearly identied (Fig.1f) as the ngerprints
12 phase55, differing from those of bulk boron with
-rhombohedral phase. Accordingly, the strong
peak at ~ 268 cm− 1 is ascribed to the out-of-plane bending vibration mode of
And the other peaks at ~ 423, ~901 and ~ 1017 cm− 1 are respectively indexed as the , and
modes, resulting from the in-plane stretching modes of
Transmission electron microscopy (TEM) was performed to determine the surface conguration of 2D
borophene sheets. A typical TEM image in Fig.2a exhibits a similar planar morphology in line with the
aforementioned SEM and AFM results (Fig.1c, d). Close examination (Fig.2a inset) reveals an ultrathin
thickness of only 6 atomic layers with an adjacent planar distance of 5.1 Å. The high-resolution TEM
(HRTEM) image further veries high-quality single crystal nature of 2D borophene sheets. As shown in
Fig.2b, the 2D borophene sheets are found to have a hexagonal honeycomb lattice with a perfect planar
≈ 2.76 Å and the intersection angle
of about 120° in the unit cell. Based on the DFT
calculations, we thus propose a novel allotrope with symmetry (referred to as
12-B5) for few-
12-borophene sheets, where there are 5 boron atoms in a unit cell (Fig.2c). In this model, both of
the lattice constants (
) of few-layer borophene are 2.83 Å and the angle
is equal to 120°, which are in good agreement with the HRTEM results (Fig.2b). Based on the theoretical
model, the bright contrasts in the HRTEM image (Fig.2b) thus correspond to the six-member rings of the
boron honeycomb lattice (Fig.2c). Besides, the layer distance of adjacent (001) planes is theoretically
calculated to be about 5.0 Å for
12-B5 borophene, nearly identical to the experimental results (5.1 Å)
measured by TEM. Statistically, the thickness of most of the 2D sheets is less than 5 nm. (Supplementary
Fig.5a). Therefore, the atomic layer numbers of the as-synthesized borophene sheets should be less than
10, unveiling the ultrathin nature of few-layer borophene. In addition, the 2D
12-borophene sheets are
thermodynamically stable as evidenced by the absence of any negative frequency in the entire Brillouin
zone (Fig.2d) according to the density functional perturbation theory (DFPT). Similar calculations are
carried out on the (104) plane (Supplementary Fig.5), which are also in good agreement with our
experimental results. High-angle annular dark-eld scanning transmission electron microscope (HAADF-
STEM) and energy dispersive X-ray spectroscopy (EDX) mapping (Fig.2e-h) images also reveal a uniform
distribution of boron element across the 2D sheet with a pure boron content over 98 %, which is in good
consistent with the electron energy loss spectrum (EELS) (Supplementary Fig.5b).
Based on all characterizations mentioned above, we can thus conclude that single crystalline few-layer
borophene sheets with
12-B5 phase were successfully synthesized using LTLE. In comparison with other
synthetic methods summarized in Supplementary Table1, our route is thus low-cost, facile and high-
ecient for scalable production of single crystalline
12-borophene sheets towards practical applications
such as Li-S battery.
To demonstrate the catalytic activity of few-layer
12-borophene sheets for Li-S battery, the potentiostatic
experiments were carried out to monitor the liquid-solid conversion in the nucleation and growth of Li2S
from polysuldes. The galvanostatic discharge was respectively performed on CNT/
(CNT/B) and bare CNT hosts at 2.05 V, in which 0.01 V overpotential was used to induce the generation
of Li2S. All the cells reached the highest potentiostatic current after about 1000 s, but the nucleation
abilities of Li2S were found to be completely different, causing a capacity of 193 mAh g− 1 and 72 mAh
g− 1 for CNT/B and CNT electrodes, respectively (Fig.3a). Besides, the dissolution ability of solid Li2S was
also remarkably promoted by the implantation of few-layer
12-borophene. After the fully conversion of
sulfurs into Li2S, the Li2S dissolution was kinetically evaluated by using a potentiostatic charge process.
Clearly, a larger oxidation current was detected on CNT/B (0.13 mA cm− 2) enabled cell in comparison
with bare CNT electrode (0.11 mA cm− 2), unveiling the excellent electrocatalysis behaviors of 2D
borophene in enhancing the dissolution of Li2S (Fig.3b).
To gain insight into the enhancement effect of
12-borophene sheets on the liquid-liquid conversion
process (Li2Sy to Li2Sx, 8 ≥ x 2, 8 ≥ y 2), Li2S8 symmetric cells were employed for the cyclic
voltammetry (CV) measurements. The CNT/B-based cell yielded a higher redox current than the bare CNT-
based cell, suggesting enhanced reactivity of the polysulde on
12-borophene interface (Fig.3c). The
kinetic-regulating role of
12-borophene was subsequently demonstrated in actual Li-S batteries. The CV
curves of the as-assembled Li-S batteries exhibited two typical redox peaks, corresponding to the
formation of soluble polysuldes (2.2–2.4 V) and solid Li2S (2.0-2.1 V), respectively. And the two
overlapped anodic peaks (2.4–2.6 V) were attributed to the sequential oxidation of Li2S and
polysuldes29. In contrast with the Li-S battery using non-undecorated CNT electrode, the Li-S battery
using CNT/B electrode possessed higher current density (Fig.3d). As shown in Fig.3e, the Tafel plots of
the rst oxidation process of the cells using CNT and CNT/B were respectively 57 and 29 mV dec− 1,
where the smaller Tafel slope of the CNT/B-based cell suggests that the
12-borophene induces higher
surface reaction rates. In addition, the simulated interfacial impedance of the Li-S cells sharply decreased
from 41.2 Ω to 24.9 Ω when the electrodes changed from CNT to CNT/B (Fig.3f), reecting the
borophene was more favorable for the interface electrochemical reactions8.
Considering the distinguished electrocatalytic reactivity and polysulde interactions of the CNT/B-based
Li-S battery in the sulfur redox reactions, their actual working performances were further evaluated by
regarding the bare CNT-based Li-S battery as a reference. In our experiments, the same amount of
polysulde (Li2S8) solution was added as active material (Supplementary Fig.6). As seen in Fig.4a, the
CV proles of CNT/B-based battery overlap each other and exhibit excellent reversibility in the redox
process, revealing the high-eciency utilization of sulfur. The galvanostatic charge/discharge proles are
shown in Fig.4b. The high reversible specic capacities of 1329, 1236, 1159, 1057, 993, and 919 mAh g−
1 were obtained at 0.3, 0.5, 1, 2, 3, and 5 C rates (1 C = 1675 mAh g− 1), respectively. Even if the current
density increased to 8 C, the CNT/B-based Li-S battery still remained an ultrahigh capacity of 721 mAh g−
1. More signicantly, after returning current density back to 0.3 C, a reversible capacity of 1216 mAh g− 1
recovered immediately with a columbic eciency of nearly 100 % (Fig.4c). By contrast, the battery using
bare CNT electrode exhibited inferior rate performances, such as a lower initial capacity of 981 mAh g− 1
at 0.3 C and a rapider degradation into 394 mAh g− 1 with the increase of capacity to 8 C as well as
unsatisfactory capacity restoration after high-rate test (Fig.4c). As shown in Fig.4d, the CNT/B-based
battery possessed a much lower polarization voltage of 188 mV than the CNT-based battery (217 mV),
further revealing the outstanding catalytic property of
12-borophene sheets for polysulde conversion.
The CNT/B cathode also exhibited excellent cycling stability at current density of 0.5 C, as found in
Fig.4e. The capacity fading rate was only 0.003% per cycle and kept nearly unvaried after 300 cycles
when the initial capacity of the CNT/B-based Li-S battery was 1110 mAh g− 1. Moreover, the CNT/B-based
cell maintained a high coulombic eciency of ~ 100% in continuous 300 cycle measurements. On the
contrary, the bare CNT-based cell delivered a low capacity of 918 mAh g− 1 and sharply decreased to 394
mAh g− 1 after 300 cycles, resulting in a fast-fading rate of 0.2 % per cycle (Fig.4e and Supplementary
Fig.7). In addition, both of the high- and low-plateau capacities of CNT/B electrode were much better
than bare CNT electrode, demonstrating few-layer
12-borophene sheets can effectively suppress the
polysulde diffusion and improve the polysulde immobilization (Supplementary Fig.9)56. Moreover,
high areal sulfur loadings of 5.3 mg cm− 2 and 7.8 mg cm− 2 with low E/S ratios of 9.8 and 6.8 ml g− 1
were respectively performed on the Li-S batteries to test the high-energy density behaviors. It was noted
that the areal capacities of the CNT/B-based Li-S cells can reach up to 4.6 and 5.2 mAh cm− 2 when the
capacities respectively adopted 871 and 661 mAh g− 1 (Fig.4f), which were much higher than those of 4.0
mAh cm− 2 for commercial Li-ion batteries57. Impressively, the CNT/B-based battery could preserve an
enough high reversible capacity of 572 mAh g− 1 with an extremely-low capacity decay rate of 0.039 % per
cycle after 1000 long-term cycles, reecting excellent cycling stability (Fig.4g and Supplementary Fig.8).
Notably, the ultralow decay rate and ultrahigh rate performance of 2D
12-borophene sheets are superior
to most of other 2D material-based Li-S batteries (Supplementary Table2), such as phosphorene (785
mAh g− 1 at 3 C, decay rate of 0.053% for 1000 cycles)30, C3N4 (340 mAh g− 1 at 4 C, decay rate of 0.5%
for 200 cycles)58, and graphene (700 mAh g− 1 at 2 C, decay rate of 0.5% for 70 cycles)59.
Finally, we calculated the adsorption energy of soluble polysuldes on a monolayer
DFT calculation to comprehend the improvement mechanism of
12-borophene sheets on Li-S batteries,
as observed in Supplementary Fig.10. Figure5a gives the optimized congurations of S8 and Li2Sn on
12-borophene sheet. Based on the DFT calculations, S8 has the weakest adsorption energy on
borophene of only 1.23 eV among all congurations, and the adsorption energy gradually increases with
the progression of the polysuldes’ lithiation and eventually arrives at 3.8 eV for the fully-lithiated Li2S
(Fig.5b). The adsorption energy of polysuldes on
12-borophene is far higher than that on CNT (below 1
eV), unveiling that
12-borophene can anchor polysulde and inhibit the shuttle of lithium polysulde
more effectively than CNT. Figure5c shows the typical partial density of states (PDOS) of Li2S4 on
12-borophene, and more details can be seen in Supplementary Fig.11. The 2p orbital
electrons of Li2S4 and
12-borophene were found to overlap near the Fermi level, suggesting the
formation of a strong chemical bonding between
12-borophene and Li2S4 cluster. This is probably
originated from a strong charge transfer of 0.22 e from
12-borophene to Li2S4 cluster (Fig.5d) based on
the charge density difference and bader charge analysis. The strong chemical interaction between
borophene and Li2S4 cluster can be also ascertained because the dark-yellow color of Li2S4 solution will
gradually attenuate with the increase of the mixing time with
12-borophene (Supplementary Fig.12).
Furthermore, the diffusion barrier of Li+ on
12-borophene was deduced to be only 0.10 eV (Fig.5e), much
lower than that (0.28 eV) on CNT (Supplementary Fig.13). The enhanced surface migration of Li+ on
borophene would further accelerate the nucleation and decomposition of Li2Sn and thus improves the
capacity and charge-discharge rate of Li-S battery60.
In summary, we have developed a novel, facile and high-yield LTLE strategy to produce single crystalline
12-borophene sheets. As promising 2D electrode materials, the
12-borophene sheets were
rstly used as ecient polysulde-conversion electrocatalysts for Li-S batteries. Due to the usage of few-
12-borophene sheets, the CNT/B
based Li-S batteries exhibited a high areal sulfur loading of 5.2
mgh cm− 2 at 7.8 mg cm− 2 under a low E/S ratio of 6.8 ml g− 1 at 0.3 C. Compared with the CNT-based Li-
S cell, the CNT/B-based Li-S cell exhibited a better rate performance of as high as 721 mAh g− 1 at 8 C
and a much lower decay rate of only 0.039 % in 1000 cycles. By DFT calculations,
12-borophene had a
lower surface diffusion barrier of Li ion and a stronger adsorption for Li2Sn clusters than CNT, which can
effectively inhibit the shuttle effect of polysuldes and accelerate their decomposition at the same time.
These should be responsible for the extraordinary catalytic activity of
12-borophene towards polysuldes
in the CNT/B-based Li-S cell. Therefore, our strategy will pave a new way for the design of high-energy
rechargeable batteries through the exploration of 2D boron-based nanomaterials.
Synthesis of few-layer β12-borophene sheets. The low-temperature liquid exfoliation (LTLE) method was
rstly developed to synthesize
12-borophene sheets at milligram scale by using boron powder (99.8 %,
Zhongnuo Incorp., China) as source materials. Firstly, 20 ~ 50 mg boron powers were added into 50 ml
N,N-Dimethylformamide (NMP, 99.9 %, Innochem. Incorp., China) to form uniform and well-dispersed
solution by several minutes’ stirring, as seen in Figure S1. Secondly, the boron-power solution was
transferred into the ethanol path and treated at -20~-25 ℃ in the tip-type ultrasonicator equipped with
cooling system (SXSONIC Incorp., China), where the ultrasonic power was kept at 800 W and the
treatment lasted for 4 ~ 8 h. Thirdly, the product solution was statically settled at room temperature for
48 ~ 72 h to enough precipitate the undissolved boron powder. Finally, the suspension was centrifuged at
about 10000 ~ 11000 revolutions per minute (rpm) for 30 minutes to obtain solid products. After the
above synthesis process, the mass of the collected 2D sheets was ranging from 4 to 10 mg. Accordingly,
the yield of 2D few-layer borophene by LTLE way can reach as high as over 20 %, which is much higher
than those by many other methods in previous reports (Supplementary Table1) 48,49.
Material characterizations. The morphology of
12-borophene sheets was investigated by SEM (Zeiss
Supra 60) and AFM (Bruker Dimension Fastscan). XPS (Thermosher Nexsa), XRD (D-MAX 2200 VPC)
and Raman spectroscope (inVia Reex, 532-nm laser) were respectively used to analyze the chemical
compositions of the sample. UV-vis spectroscopy (UV-3600) was applied to determine the energy-band
structure and absorption coecient of
12-borophene sheets. TEM and HRTEM (FEI Titan 80–300) were
employed to ascertain the lattice structure of the product. The STEM and elemental mapping were
performed on a JEM ARM200F thermal-eld emission microscope with a probe Cs-corrector working at
200 kV. For the HAADF imaging, the convergence angle of ~ 23 mrad and collection angle range of 68 ~
174 mrad were adopted for the incoherent atomic number imaging. Both the elemental composition and
distribution were analyzed on the energy dispersive X-ray analyzer (EDS, EX-230 100m2 detector)
equipped with the microscope.
Preparation of Li 2 S 8 catholyte. The sources of sulfur and Li2S with a molar ratio of 7:1 were put into an
appropriate amount of 1 mol l− 1 lithium bis (triuoromethanesulfonyl) imide (LiTFSI). Secondly, the LiTFI
solution was added into the mixed solvent of 1,3-dioxolane (DOL) and 1,2-dimethoxyethane (DME)
(volume ratio (
): 1:1). Thirdly, 1
% LiNO3 was used as additive by vigorous magnetic stirring at 50
℃ until the sulfur powder were fully dissolved. The concentration of Li2S8 was ranging from 0.15 to 2
mol l− 1.
Fabrication of CNT electrodes. 5 g commercial multiwalled CNT (length ~ 50 nm, Aladdin, China) powders
were dispersed into 50
Triton X-100 aqueous solution (0.01
%, Secco Romeo, China) to form
uniform and homodisperse solution by ultrasonication for 2 h. Subsequently, the obtained CNT solution
was ltered through nylon lm under vacuum. After three-time washing by deionized water and drying for
2 h at 60 ℃ in vacuum oven, the free-standing CNT paper was peeled from the nylon lm. Finally, the
obtained CNT paper was cut into desired disks as the free-standing electrode.
Assembly of symmetric cells for kinetic evaluation of polysulde conversion. CNT/B (with a mass
loading of about 1 mg
12-borophene sheets) or bare CNT electrodes were used as both working and
counter electrodes. And 40 µl catholyte (0.5 mol l− 1 Li2S6 and 1.0 mol l− 1 solution of LiTFSI with 1
LiNO3 in DOL and DME,
= 1:1) was added into each coin cell. The CV behaviors of the symmetric cell
were tested at a scan rate of 10 mV s− 1, in which the voltage window ranged from − 0.8 to 0.8 V.
Measurement on the nucleation and dissolution of Li 2 S. The CNT/B or CNT lm electrodes were used as
cathodes and Li foils were employed as the anodes. Also, 20
Li2S8 solution (0.15 mol l− 1) was applied
as catholyte, and 20 µl electrolyte without Li2S8 was used as anolyte. For the nucleation and growth of
Li2S, the assembled cells were rst discharged galvanostatically to 2.06 V at 0.112 mA, and then
discharged potentiostatically to 2.05 V until the current dropped to below 10− 5 A. The deposition
capacities of Li2S were calculated according to the Faraday’s law. For the Li2S dissolution, the assembled
cells were rstly galvanostatically discharged to 1.80 V at 0.10 mA, and subsequently galvanostatically
discharged to 1.80 V at 0.01 mA for fully transforming sulfur species into solid Li2S. Then the cells were
potentiostatically charged at 2.40 V to oxidize Li2S into soluble polysuldes. The potentiostatic charge
was accomplished when the charge current was below 10− 5 A.
Assembly and performance evaluation of Li–S cells. CR-2016 coin cells were assembled in an argon-
protected glove box, where the CNT/B or CNT lms were employed as the cathodes and 20 µl Li2S8
catholyte was dropped onto the CNT lm as the sulfur cathode. Also, Li foil was applied as the counter
electrode, and 1.0 M solution of LiTFSI with 1
% LiNO3 in DOL and DME (
= 1:1) was used as the
electrolyte. In experiments, the common areal loading of sulfur was about 1 mg cm− 2, and the
electrolyte/sulfur ratio was xed at 15 µl mg− 1. The electrochemical performances of Li-S batteries were
measured by a LANDCT2001A analyzer, where the voltage interval ranged from 1.7 to 2.8 V. And the
cyclic voltammograms (CV) curves were collected at 0.1 mV s− 1on a CHI-760E electrochemical
workstation (Chenhua Instrument, Shanghai), in which EIS analysis was in the range of 10 kHz-0.01 Hz.
Theoretical model of few-layer β12-borophene sheets. All the calculations except superconducting
properties were carried out using Vienna
simulation package (VASP 5.4)61,62 with projector
augmented wave (PAW) pseudopotential method63,64 and Perdew-Burke-Ernzerhof (PBE) functional65.
Both lattice parameters and atomic positions were optimized by conjugate gradient method, and the
convergence criteria for energy and force were eV and eVÅ-1, respectively. The
kinetic energy cutoff for plane waves was set at 450 eV. The Brillouin zones were sampled with
Å-1 spacing in reciprocal space by the Monkhorst-Pack scheme66. The high symmetry K-
points for band structure and phonon dispersion curves were generated by AFLOW package67. And
Grimme’s DFT-D3 van der Waals corrections with the Becke-Jonson damping68,69 was employed. The
phonon spectrum was calculated by DFPT method implemented in Phonopy program69. Also, the crystal
structures were visualized by VESTA package70.
Computational methods of the adsorption energy of few-layer β12-borophene. First-principle calculations
were implemented using VASP61 software package. The PBE65 functional of generalized gradient
approximation (GGA) was used for the exchange-correlation. The basis set utilized PAW pseudopotential
method63,64, and the energy cutoff was set at 400 eV. The self-consistent eld (SCF) tolerance was
eV and the force convergence criterion for atomic relaxation was 0.02 eV Å−1. A Monkhorst-
Pack k-point mesh with different sizes was chosen to meet various requirements, where is
for the geometrical relaxation, is for the calculation of electronic structure and
is for the calculation of adsorption. The vdW forces between Li2Sn and
12-borophene sheet or CNT were
accurately obtained by the DFT-D3 method68. The supercell of
CNT was used for the adsorption energy and CI-NEB calculations, respectively. The adsorption energy (
) was derived using the following equation:
The authors declare that all the data supporting the ndings of this study are available within the article
and its Supplementary Information or from the corresponding authors upon reasonable request.
The authors are very thankful for the support of the National Science Foundation of China (Grant Nos.
51872337, 51872283, 22075279, 21872145), National Project for the Development of Key Scientic
Apparatus of China (2013YQ12034506), National Key Research and Development Program of China
(Grant no. 2019YFA0210203, 2016YFB0100100, 2016YFA0200200), the Fundamental Research Funds
for the Central Universities of China, the Science and Technology Department of Guangdong Province
and the Education Department of Guangdong Province, the Liao Ning Revitalization Talents Program
(Grant XLYC1807153), the Natural Science Foundation of Liaoning Province, Joint Research Fund
Liaoning-Shenyang National Laboratory for Materials Science (Grant 20180510038), Dalian Science and
Technology Bureau (2019RT09), Dalian National Laboratory For Clean Energy (DNL), CAS, DNL
Cooperation Fund, CAS (DNL180310, DNL180308, DNL201912, and DNL201915), DICP (DICP
ZZBS201708, DICP ZZBS201802, DICP I2020032), DICP&QIBEBT (Grant DICP&QIBEBT UN201702),
GFKJCXTQ Foundation (Grant 18-163-14-ZT-002-001-02).
B. Y., Z. -S. W. and F. L. proposed and supervised the projects. H.J.L. synthesized the borophene sheets,
and characterized their surface morphology and chemical compositions. H. D. S. fabricated the CNT- and
CNT/B-based Li-S batteries, and carried out the electrochemical measurements. Z. W. carried out the TEM
analysis of the borophene sheets and calculated the adsorption energies of Li2Sn clusters on monolayer
borophene or CNT by DFT model. Y. W. M. proposed the DFPT model of the surface conguration of the
12-borophene. H. J. L., H. D. S, Z. W., Y. W. M., S. D. L., B. Y., Z. -S. W. and F. L. wrote the paper. All the
authors involved in the analysis and discussion of the experimental results. And all authors approve to
submit the nal version of the manuscript.
Supplementary Information accompanies this paper at http://www.nature.com/naturecommunications
Competing nancial interests: The authors declare no competing nancial interests
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